Athletic shoes, especially those used for running, should be both lightweight and durable. The outsoles of such shoes should be able to withstand the wear caused by many miles of training, and yet be flexible and not cause the shoe to be unacceptably heavy. Recent efforts have included searches for materials with desirable durability, flexibility, and weight. But outsole wear remains a problem which often limits the life of the shoe.
Another important characteristic of an outsole is its traction. Often materials which provide adequate traction for some running surfaces, e.g., dry blacktop, do not perform as well on others, e.g., dirt, wood, or wet blacktop. It would be desirable to have an outsole which provides optimum traction on all types of running surfaces and for all kinds of weather conditions.
Yet another important role of the outsole is its contribution to cushioning and to other properties of the shoe that affect the shoe's performance with respect to the specific biomechanical requirements of the user. One approach has been to customize the shoe to meet the needs of the individual by inserting specially designed orthotics inside the shoe. Such orthotics are generally difficult to fit and expensive.